Throughout this application various publications are referred to by Arabic numerals in parentheses. Full citations for these references may be found at the end of the specification immediately preceding the claims. The disclosures of these publications are hereby incorporated by reference in their entireties into the subject application to more fully describe the art to which the subject application pertains.
Pseudomonas aeruginosa is a Gram-negative bacterium found in a wide range of environments including water, soil, and mammals (1). It is a major opportunistic human pathogen, infecting burns, and lungs in cystic fibrosis (2). Compromised immune systems and extended hospitalization are correlated with infections, making P. aeruginosa the causative agent of approximately 15% of all hospital infections (2, 3). P. aeruginosa infections are difficult to treat since the bacterium has multiple antimicrobial resistance mechanisms (4). Chronic infections can be severe in patients with cystic fibrosis, causing high rates of morbidity and mortality (5, 6). P. aeruginosa infections are related to quorum sensing (QS) pathways, which regulate virulence factors and biofilm formation.
Signal molecules of QS include N-acyl-homoserine lactones (AHLs). The concentration of AHLs increases during bacterial growth to allow AHL binding to specific receptors and the regulation of target genes. In P. aeruginosa, the las and rhl QS systems use AHLs of 3-oxo-C12-homoserine lactone and C4-homoserine lactone as signal molecules, respectively. Microarray studies on P. aeruginosa indicated that QS regulated 3-7% of the total open reading frames (7-9). Deletion of single or multiple QS genes reduced the virulence of P. aeruginosa in mouse studies, indicating a strong correlation between the QS system and P. aeruginosa pathogenesis (10-15). Quorum sensing blockade does not affect bacterial growth and is therefore expected to attenuate the virulence of infection without causing drug resistance (16, 17).
Potential therapeutic targets in the QS system include enzymes involved in the formation of AHLs that act as signaling molecules and as virulence factors in P. aeruginosa (16). AHLs are synthesized from S-adenosylmethionine (SAM) and acylated-acyl carrier protein by AHL synthase with 5′-methylthioadenosine (MTA) as a by-product. MTA is recycled to ATP and methionine for SAM recycling (17). In bacteria, 5′-methylthioadenosine nucleosidase (MTAN) is the normal path to produce adenine and 5-methylthioribose-α-D-1-phosphate (MTR-1-P) from MTA for recycling. Transition state analogue inhibitors of E. coli and V. cholerae MTAN disrupted quorum sensing and reduced biofilm formation, supporting MTAN as a target for QS (17).
With the growing global threat of multi-drug resistance, nonconventional antibacterial discovery approaches are required that are nonlethal to bacteria where the potential to develop drug resistance is assumed to be less significant. The present invention addresses that need for infections caused by bacteria such as Pseudomonas aeruginosa that use 5′-methylthioinosine phosphorylase (MTIP) in a quorum sensing pathway.